Investment Securities - Summary of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Amortized Cost, Held-to-maturity	$ 4,054
Due after one year through five years, Amortized Cost, Held-to-maturity	280,057
Due after five years through ten years, Amortized Cost, Held-to-maturity	133,106
Due after ten years, Amortized Cost, Held-to-maturity	669,767
Total Held-to-maturity, Debt Maturities, Amortized Cost Basis	1,086,984
Due in one year or less, Fair Value, Held-to-maturity	4,086
Due after one year through five years, Fair Value, Held-to-maturity	288,032
Due after five years through ten years, Fair Value, Held-to-maturity	134,081
Due after ten years, Fair Value, Held-to-maturity	659,282
Total, Held-to-maturity, Fair Value	1,085,481
Due in one year or less, Amortized Cost, Available-for-sale	4,821
Due after one year through five years, Amortized Cost, Available-for-sale	2,368,827
Due after five years through ten years, Amortized Cost, Available-for-sale	393,699
Due after ten years, Amortized Cost, Available-for-sale	30,643
Amortized Cost, Available-for-sale	2,797,990	$ 2,344,174
Due in one year or less, Fair Value, Available-for-sale	4,920
Due after one year through five years, Fair Value, Available-for-sale	2,383,641
Due after five years through ten years, Fair Value, Available-for-sale	392,160
Due after ten years, Fair Value, Available-for-sale	31,627
Total Available-for-sale Securities, Debt Maturities, Available-for-sale, Fair Value	$ 2,812,348	$ 2,398,923